1. Field
One embodiment of the invention relates to a communication interface circuit which transmits a signal to or receives a signal from a communicatee device, an electronic device including the communication interface circuit, and a communication method.
2. Description of the Related Art
In recent years, with improvement of processing ability of a computer, high-speed data transfer is required for an interface with a peripheral device. As an interface standard with a storage device such as an HDD (Hard Disk Drive), the SAS (Serial Attached SCSI) standard which is one of SCSI (Small Computer System Interface) standards has prevailed. Although a conventional SCSI standard employs a parallel transfer scheme, the SAS standard employs a serial transfer scheme to make it possible to perform high-speed and high-precision data transfer.
In an SAS interface, as a process of establishing a connection between a transmission side and a reception side, search for communicatee is performed by a burst signal called OOB (Out Of Band). When the communicatee is found, speed negotiation is performed to determine a transfer speed between the transmission side and the reception side. When the communication is established as described above, the SAS interface is set in an idle state which waits for transmission/reception of a command.
In the idle state, in order to maintain a connection established state, the transmission side and the reception side must keep outputting predetermined signals. For this reason, in the idle state, although a command or data is not transmitted or received, electric power is disadvantageously consumed. In the SAS standard, power saving in the idle state is not regulated. In a conventional idle state, for example, in order to cope with various communication environments such as an attenuation level of a transmission signal on a transmission path, a signal is transmitted at a voltage of about 1.2 V equal to that in a normal state which performs command transmission and reception. For this reason, a large power consumption in the idle state is posed as a problem.
Some information processing devices using an interface of the S-ATA (Serial-ATAttachment) standard lower a power of an interface for connecting a south bridge to an HDD in a host when data transmission/reception is not performed for a predetermined period of time (for example, Jpn. Pat. Appln. KOKAI Publication No. 2006-18388).
In some power management technique for an HDD, repeaters are arranged between a controller and a plurality of HDDs which are hierarchically arranged and have different performances, and a function to stop and start the HDDs according to predetermined conditions is given to the repeaters (for example, Jpn. Pat. Appln. KOKAI Publication No. 2008-41050).
As in the SAS standard, in an interface which must keep transmitting and receiving a signal to maintain a connection after the connection is established, suppression of a power consumption in the transmission/reception of the signal is posed as a problem.